Electric capacitor cooling means

ABSTRACT

1,045,835. Capacitors. GENERAL ELECTRIC CO. Aug. 13, 1963 [Sept. 18, 1962], No. 31964/63. Heading H1M. In the capacitor shown in cross-section, the side walls 2a and 2b of casing 2 are flexible to respond to expansion or contraction of the dielectric fluid 15, and heat-conducting plates 11 and 12 having portions 11a and 12a in constant contact with the capacitor transfer heat therefrom to the end walls 2c and 2d of the casing. The inwardly bowed members 11 and 12 may also have portions projecting outwardly to contact side walls 2a and 2b to maintain the spacing between the conducting plates and the side walls, and the contact of the heat-conducting members with the capacitor unit. Alternatively, as in Fig. 4 (not shown), these results are achieved by appropriately located leaf or coil springs. Plates 11 and 12 may have apertures to facilitate circulation of the dielectric fluid and are preferably of metal having high thermal conductivity, e.g. aluminium. Outer casing 2 is preferably of metal, such as mild or stainless steel, having a coefficient of expansion lower than that of the plates 11 and 12. The capacitor unit shown comprises flattened rolls surrounded by insulation 10, the casing 2 being hermetically sealed by a cover. The dielectric fluid may be chlorinated diphenyl, insulating oil or sulphur hexafluoride.

N 1965 J. H. WURSTER ELECTRIC CAPACITOR COOLING MEANS 2 Sheets-Sheet 1Filed Sept. 18, 1962 Join E Wars/6% Nov. 23, 1965 J, H. WURSTER3,219,892

ELECTRIC CAPACITOR COOLING MEANS Filed Sept. 18, 1962 2 Sheets$heet 2 20I l l 160 200 2 10 zz'so 3210 [22 @2761;

14/0775 m 1? wsz United States Patent 3,219,892 ELECTRIC CAPACITORCOOLING MEANS John H. Wurster, Moreen, N.Y., assignor to GeneralElectric Company, a corporation of New York Filed Sept. 18, 1962, Ser.No. 224,333 Claims. (Cl. 317-243) The present invention relates tocooling arrangements especially for electrical devices, and moreparticularly relates to electrical capacitors having improved heatdissipation characteristics.

The efficient removal of heat from capacitors during operation has beenrecognized as essential in order to obtain satisfactory lifecharacteristics and thermal stability of the units. Also, it isdesirable to maintain internal pressure in the capacitors at a suitablelevel under low temperature conditions so as to retain high resistanceto corona under such conditions.

However, the prior capacitor constructions have not provided fullysatisfactory results in the respects mentioned. In a conventionaldesign, the capacitor sections are arranged in a tight fit within theouter casing in order to provide good conduction of heat from theinterior sections to the casing, but in such arrangements when thecapacitor cools down under low temperature conditions, low pressureconditions develop in the capacitor because the casing walls areprevented by such tight fitting sections from contracting inwardly asthe dielectric liquid contracts. On the other hand, while looselyfitting capacitor sections enable the attainment of better lowtemperature corona strength, such an arrangement has reduced heattransfer capability and causes the dielectric to operate at excessivelyhigh temperatures, resulting in poor life of the capacitors.

It is an object of the invention to provide sealed electrical devices,and especially electrical capacitors, which avoid the abovedisadvantages of prior art constructions.

It is another object of the invention to provide electrical capacitorsor the like having improved heat dissipation characteristics under hightemperature conditions so as to prolong their life and impart improvedthermal stability, while maintaining good electrical characteristics ofthe capacitors under low temperature conditions.

It is still another object of the invention to provide simple andeconomical means to improve the heat dissipating characteristics ofpower capacitors or the like when mounted in banks of capacitors inclose proximity to one another.

Other objects and advantages will become apparent from the followingdescription and the appended drawings.

With the above objects in view, the present invention in a preferredembodiment relates to an electrical capacitor comprising a containerhaving a pair of opposite side walls adapted to flex with variation intemperature and opposite end walls joining the side walls, dielectricliquid in the container in which a capacitor pack is immersed and whichproduces heat during operation of the capacitor, the capacitor packbeing spaced from the opposite side walls of the container so as todefine therewith spaces occupied by the dielectric liquid, and heatconducting plate means arranged between the capacitor pack and thecontainer side walls having main portions in the spaces in constantcontact with the capacitor pack and having other portions adjacent thecontainer end walls, whereby during operation of the capacitor the platemeans 3,219,892 Patented Nov. 23, 1965 "ice transfers heat from thecapacitor pack to the container end walls, and the container side wallsare free to flex inwardly into the spaces described during thermalcontraction of the dielectric liquid therein.

The invention will be better understood from the fol lowing descriptiontaken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view, partly broken away, of an electricalpower capacitor embodying the invention;

FIGURE 2 is a perspective view of one of the heat transfer membersemployed in the FIGURE 1 device in accordance with the invention;

FIGURE 2a is a view in vertical section of a modified form of heattransfer member;

FIGURE 2b is a view in vertical section of another modified form of heattransfer member;

FIGURE 3 is a cross-sectional View of the FIGURE 1 device taken alongthe line 3-3;

FIGURE 4 shows a similar cross-sectional view of a modfied arrangement;

FIGURES 5, 6 and 7 are diagrammatic views showing various forms of heattransfer members which may be employed in accordance with the invention;and

FIGURE 8 is a graphical showing of the improved properties provided bythe invention as compared to prior art devices.

Referring now to the drawings, and particularly to FIGURE 1, there isshown a power capacitor 1 comprising a rectangular metal container orcasing 2 containing capacitor pack 3 made up of a plurality of flattenedroll sections 4, each of which is formed of a pair of electrode foilsinterwound with dielectric sheets in a manner well-known in the art.Each roll section 4 has electrode terminal tabs 5 and 6 connected to therespective electrode foils and projecting from the upper ends of thecapacitor roll section. The terminal tabs are suitably electricallyconnected to leads (not shown) which extend through terminal bushings 7and 8 mounted on cover 9'. Instead of having terminal tabs as described,the capacitor roll sections may be of exposed foil arrangement Wellknownin the art, in which the foil armatures project from opposite ends ofthe roll and leads are suitably attached to the exposed foils. Capacitorpack 3 is wrapped in a covering of insulating material 10, referred toherein as major insulation, such as one or more layers of kraft paper,which separates pack 3 from metal casing 2. Casing 2 is hermeticallysealed by cover 9 and contains a dielectric liquid such as chlorinateddiphenyl, mineral oil or the like, in which capacitor pack 3 is immersedand which impregnates the dielectric paper sheets thereof. Instead ofbeing a liquid, the dielectric medium may be a gas, such as sulfurhexafluoride.

In accordance with the invention, there are provided in casing 2, asbest seen in FIGURE 3, heat transfer plates 11 and 12 having a heightapproximately thesame as capacitor pack 3 and shaped as shown in FIGURE2, the plates being arranged between the casing walls and majorinsulation 10 substantially surrounding the insulated capacitor pack,and normally resting on the bottom of the casing. Each plate 11, 12 ispreferably made of a metal of high thermal conductivity such asaluminum, and comprises, as shown in the FIGURE 2 embodiment, aninwardly bowed main portion 11a and flange portions 11b, 11c projectingtherefrom. The dimensions of each plate 11, 12 are such that whenassembled in casing 2 the the plates fit snugly between the opposite endwalls 2c, 2d of casing 2 with their flange portions 11b, 11c and 12b,120 in contact with or in close proximity to the respective end walls,and with the bowed plate portions 11a, 12a pressing inwardly in constantcontact with opposite sides of insulated capacitor pack 3 as shown inFIGURE 3. Capacitor pack 3 is usually of sufficient length such that theflange portions of plates 11, 12 fit tightly between the ends of thecapacitor pack 3 and the adjacent end walls of casing 2. In a preferredembodiment, the broad sides 2a, 2b of casing 2 are bowed somewhatoutwardly as shown in FIGURE 3, for reasons explained hereinafter.

By virtue of the arrangement described, plates 11 and 12 are incontinuous contact through major insulation with the central portions ofcapacitor pack 3, which normally are the hottest portions during theoperation of the capacitor, and plates 11, 12 will conduct the heat fromthese areas to the normally cooler end walls 2c, 2d and the bottom ofeasing 2. Since capacitors of this type are frequently mounted in bankswith their broad sides facing one another in close proximity, the heatdissipation problem in the use of conventional power capacitors isespecially troublesome because in such units, as indicated, the broadside walls are usually the hottest portion of the casing and radiate theheat toward one another. The transference of heat to the cooler endwalls and bottom of the outer casing as effected by the cooling platearrangement of the invention thus largely overcomes this problem and byobtaining thereby lower dielectric temperatures in the capacitor, longerlife and better thermal stability of the capacitor are achieved.

In the described arrangement, spaces 13 and 14 occupied by dielectricliquid 15 are defined between the inwardly bowed cooling plates 11, 12and the adjacent outwardly bowed broa'd side walls 2a, 2b of casing 2,the size of the spaces depending on the extent of outward bowing of sidewalls 2a, 2b and the difference in width between capacitor pack 3 andthe casing. The presence of spaces 13, 14 makes it possible for thebroad side walls 211, 2b of the casing to flex inwardly during coolingof the capacitor following the contraction of the dielectric liquid 15during such cooling. As a result, the drop in internal pressure whichwould otherwise occur if inward flexing of the broad side walls of thecasing is prevented by a tightly fitting capacitor pack is considerablyreduced, and the problem of low corona strength attendant on lowinternal pressure is thereby overcome. Moreover, the dielectricreservoir in spaces 13 and 14 aids in the cooling of capacitor pack 3,since the dielectric liquid 15 therein will circulate by convection inthese spaces and transfer heat from the normally hotter central portionsto the cooler end walls and bottom of capacitor casing 2. This means ofheat transfer improves as the capacitor becomes hotter due, for example,to voltage increase.

If desired, plates 11, 12 may be modified to facilitate circulation ofdielectric liquid in spaces 13, 14 from one side of each plate to theother by providing apertures or cutout portions in the body or at thetop or bottom of the plates.

Advantageously, cooling plates 11, 12 have a thermal expansioncoefficient greater than that of the metal of easing 2, since under suchconditions the pressure of plates 11, 12 on capacitor pack 3 increaseswith increasing temperature due to the more rapid expansion of theplates as compared to the casing walls, Such results are obtained, forexample, when the plates are made of aluminum and the casing metal ismild steel or stainless steel. The increased pressure of the plates onthe capacitor pack improves heat transference from the pack to theplates and then to the capacitor end walls, and thereby further reducesthe operating temperature of the capacitor pack.

FIGURE 2a shows in vertical cross-section a modified form of the heattransfer plate shown in FIGURE 2 which comprises a similarl inwardlybowed main portion 11d having outwardly projecting bosses He and 11which when the plate is assembled in case 2, press against the innersurface of the container side wall. Bosses 11e, 11 thus serve to ensureconstant contact of the heat transfer plate against capacitor pack 3 andmaintain the reservoir space for the dielectric liquid 15. The bossesare preferably arranged near the top and bottom of the heat transferplate so that they contact the container side wall near its cooler topand bottom portions and thereby improve the heat transfercharacteristics, while at the same time they do not interfere with theinward flexing of the container side wall in view of their location awayfrom the central portion of the latter.

FIGURE 2b shows another modification of the heat transfer plates whereinthe bowed center portion of the plate has an inwardly dished centralregion 11g. In operation, the outside rim 1112 of the heat transferplate presses in direct contact with the container side wall and thecentral dished portion 11g presses against capacitor pack 3. There isthereby provided additional assurance that the heat transfer plates willremain in constant contact with the sides of capacitor pack 3 and thatthe dielectric liquid reservoirs between the pack and container sidewall will be maintained.

FIGURE 4 shows a modification of the FIGURE 3 device which includesrecesses or channels 16 and 16a formed in the side walls of casing 2dfor retaining leaf springs 17, 17a bearing with their convex surfacesagainst the central portions of bowed cooling plates 11a, 12a, and withtheir ends against casing 2d, thereby providing increased pressure ofthe plates against the capacitor pack, and also adding to the dielectricliquid reservoir space. Coil springs or other equivalent resilientmembers could be employed instead of leaf springs if desired.

FIGURE 5 shows a variation in the form of the cooling plates wherein thecooling plate means are constituted by an integral tubular member orsleeve 19 having inwardly bowed broad side portions joined by straightend portions, tubular member 19 being proportioned to snugly fit withinthe outer capa-ctor casing and against the capacitor pack inserted inits interior space.

FIGURE 6 shows another embodiment comprising a pair of angular plates20, 21 each formed with .a bowed main portion and a single straightflange portion at an angle thereto, so that when assembled as shown thetwo plates together encompass and press against the capacitor packsubstantially as in the FIGURE 3 embodiment.

FIGURE 7 shows still another modification wherein the plates are formedof telescoping U-shaped members 22, 23 with their web portions atopposite ends and with their arms bowed inwardly as shown. Such anarrangement may be fitted within capacitor casings of various widthssimply by extending or retracting the telescoped members relative to oneanother.

Tests were made comparing temperature rises for standard capacitors andsimilar capacitors incorporating cooling plates constructed and arrangedin accordance with the invention. FIGURE 8 is a graph showing theresults of these tests, the graph plotting the temperature in C. againstwatts loss. In tests tests, a group of each type of unit were mountedwith their broad sides facing one another at a spacing of 2% inchesbetween cases and were operated in an ambient temperature of about 45 C.The curves in the graph represent the following:

Curve A-maximum dielectric temperaturestandard unit Curve A'maximumdielectric temperaturecooling plate unit Curve B-average dielectrictemperaturestandard unit Curve B'-average dielectric temperaturecoolingplate unit Curve Cmaximum case temperaturestandard unit Curve Cmaximumcase temperaturecooling plate unit 7 As is evident from the graph, ineach of the temperature categories measured, the capacitors equippedwith a cooling plate arrangement in accordance with the invention werecharacterized by a substantially lower temperature than the standardunits. At 220 watts, for example, the maximum dielectric temperature(i.e., hot spot temperature) of the units of the invention was about 11/2 C. less than that of the standard units.

The heat transfer plate arrangement of the invention has a number ofadvantages in addition to those already mentioned. They may, forexample, serve as a holding device or tunnel to facilitate assembly ofthe capacitor pack and major insulation in the outer container. Thecooling plates not only assist in removing the heat from the capacitorsduring operation, but they also assist in introducing the necessary heatinto the capacitor elements during the usual treating process employedin manufacture of the capacitors. When made of aluminum, the platesimprove the quality of the dielectric liquid due to the getter action ofthe aluminum oxide film normally present on the aluminum, by whichelectrically deleterious particles are removed from the liquid.

While the invention has been described particularly with respect topower capacitors, it is evident that it has application to other typesof capacitors such as high energy storage capacitors, pulse formingcapacitors, and other electrical devices, and also to apparatus ingeneral where the dissipation of heat from the apparatus is a problem.

While the present invention has been described with reference toparticular embodiments thereof, it will be understood that numerousmodifications may be made by those skilled in the art without actuallydeparting from the scope of the invention. Therefore, the appendedclaims are intended to cover all such equivalent variations as comewithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Electrical capacitor comprising a container having a pair of oppositeside walls and a pair of opposite end walls joining said side walls, adielectric fluid in said container, a capacitor pack which produces heatduring operation thereof in said dielectric fluid thereby causingthermal expansion and contraction of said dielectric fluid, saidcapacitor pack being spaced from said opposite side walls of saidcontainer so as to define therewith spaces occupied by said dielectricfluid, said container side walls being free to flex inwardly into saidspaces during thermal constration of said dielectric fluid, and metalheat conducting means arranged between said capacitor pack and saidcontainer having main portions in said spaces in constant contact withsaid capacitor pack and having other portions in physical contact withsaid container end walls, whereby during operation of said capacitorpack said heat conducting means transfers heat therefrom to saidcontainer end walls.

2. Electrical capacitor comprising a container having a pair of oppositeside walls and a pair of opposite end walls joining said side walls, adielectric liquid in said container, a capacitor pack which producesheat during operation thereof immersed in said dielectric liquid therebycausing thermal expansion and contraction of said dielectric liquid,said capacitor pack being spaced from said opposite side walls of saidcontainer so as to define therewith spaces occupied by said dielectricliquid, said container side walls being free to flex inwardly to saidspaces during thermal contraction of said dielectric liquid, and metalheat conducting plate means arranged between said capacitor pack andsaid container having main portions in said spaces in constant contactwith said capacitor pack and having other portions in physical contactwith said container end walls, whereby during operation of saidcapacitor pack said heat conducting plate means transfers heat from saidcapacitor pack to said container end walls.

3. Electrical capacitor comprising a rectangular container having a pairof opposite side walls adapted to flex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack including aninsulating covering thereon immersed in said dielectric liquid andspaced from said opposite container side walls so as to define therewithspaces occupied by said dielectric liquid, said capacitor pack producingheat during operation thereof, and heat conducting metal plate meansarranged between said capacitor pack and said container substantiallysurrounding said capacitor pack, said metal plate means having mainportions in said spaces in constant contact with said capacitor pack andhaving other portions adjacent said container end walls, whereby duringoperation of said capacitor said metal plate means transfers heat fromsaid capacitor pack to said container end walls and said container sidewalls are free to flex inwardly into said spaces during thermalcontraction of the dielectric liquid therein.

4. Electrical capacitor comprising a rectangular container having a pairof opposite side walls adapted to flex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack including aninsulating covering thereon immersed in said dielectric liquid andspaced from said opposite container side walls so as to define therewithspaces occupied by said dielectric liquid, said capacitor pack producingheat during operation thereof, and heat conducting metal plates arrangedbetween said capacitor pack and said container substantially surroundingsaid capacitor pack, said metal plates having inwardly dished centralportions in said spaces in constant contact with said capacitor pack andhaving other portions adjacent said container end walls, whereby duringoperation of said capacitor said metal plates transfer heat from saidcapacitor pack to said container end walls and said container side wallsare free to flex inwardly into said spaces during thermal contraction ofthe dielectric liquid therein.

5. Electrical capacitor comprising a rectangular container having a pairof opposite side walls adapted to flex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack including aninsulating covering thereon immersed in said dielectric liquid andspaced from said opposite container side walls so as to define therewithspaces occupied by said dielectric liquid, said capacitor pack producingheat during operation thereof, and heat conducting metal plates arrangedbetween said capacitor pack and said container substantially surroundingsaid capacitor pack, said metal plates having main portions in saidspaces in constant contact with said capacitor pack and having otherportions adjacent said container end walls, the main portions of saidmetal plates having outwardly projecting portions in contact with saidcontainer side walls for maintaining said main portions in constantcontact with said capacitor pack while spacing said main portions fromsaid container side walls, whereby during operation of said capacitorsaid metal plates transfer heat from said capacitor pack to saidcontainer end walls and said container side walls are free to flexinwardly into said spaces during thermal contraction of the dielectricliquid therein.

6. An electrical capacitor as defined in claim 3, wherein said metalplate means comprises a pair of plates having main portions between therespective container side walls and said capacitor pack and flangeportions between the respective container end walls and said capacitorpack, said main portions being bowed inwardly and in constant contactwith said capacitor pack.

7. An electrical capacitor as defined in claim 3, wherein said metalplate means comprises an integral rectangular tubular member havingopposite main portions between the respective container side walls andsaid capacitor pack and end portions between the respective containerend walls and said capacitor pack, said main portions being bowedinwardly in constant contact with said capacitor pack.

8. An electrical capacitor as defined in claim 3, wherein said metalplate means comprises a pair of angular plates each having a mainportion between the respective side wall and said capacitor pack and aflange portion between the respective end wall and said capacitor pack,each main portion being bowed inwardly in constant contact with saidcapacitor pack.

9. An electrical capacitor as defined in claim 3 wherein said metalplate means comprises a pair of U-shaped members arranged incomplementary telescoping relation at their open ends with the armportions thereof arranged between the respective container side wallsand said capacitor pack and the Web portions thereof between therespective end walls and said capacitor pack, the arm portions beingbowed inwardly in constant contact with said capacitor pack.

10. An electrical capacitor comprising a container having a pair ofopposite side walls, a pair of opposite end walls joining said sidewalls, a top, and a bottom, said side walls being adapted to flex withvariations in temperature of the capacitor and being normally bowedoutwardly, a dielectric liquid in said container, a capacitor packimmersed in said dielectric liquid and adapted to produce heat duringoperation thereof, said capacitor pack comprising a plurality of woundcapacitor roll sections arranged with their axes parallel to thecontainer side walls, said capacitor pack being spaced from saidopposite side walls so as to define therewith spaces occupied by saiddielectric liquid, and heat conducting metal plate means arrangedbetween said capacitor pack and said container and substantiallysurrounding said capacitor pack, said metal plate means having mainportions in said spaces in constant contact with said capacitor pack andother portions adjacent said container end walls, whereby duringoperation of the capacitor said plate means transfers heat from saidcapacitor pack to said container end walls and the container side wallsare free to flex inwardly into said spaces during thermal contraction ofthe dielectric liquid therein.

11. Electrical capacitor comprising a rectangular metal container havinga pair of opposite side walls adapted to flex with variation incapacitor temperature and opposite end walls joining said side walls, adielectric liquid in said container, a rectangular capacitor packincluding insulating covering thereon immersed in said dielectric liquidand adapted to produce heat during operation thereof, said capacitorpack being spaced from said opposite container side walls so as todefine therewith spaces occupied by said dielectric liquid, and heatconducting metal plate means composed of metal having a highercoefficient of thermal expansion than said metal container and arrangedbetween said capacitor pack and said container substantially surroundingsaid capacitor pack, said metal plate means having main portions in saidspaces in constant contact with said capacitor pack and other portionsadjacent said container end walls, whereby during operation of thecapacitor said metal plate means transfers heat from said capacitor packto said container end walls and said container side walls are free tofiex inwardly into said spaces during thermal contraction of thedielectric liquid therein.

12. Electrical capacitor comprising a rectangular container having apair of opposite side Walls adapted to flex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack includinginsulating covering thereon immersed in said dielectric liquid andadapted to produce heat during operation thereof, said capacitor packbeing spaced from said opposite container side walls so as to definetherewith spaces occupied by said dielectric liquid, heat conductingmetal 53 plate means arranged between said capacitor pack and saidcontainer substantially surrounding said capacitor pack, said metalplate means having main portions in said spaces in constant contact withsaid capacitor pack and other portions adjacent said container endwalls, and means urging said main portions in constant contact with saidcapacitor pack, whereby during operation of said capacitor said metalplate means transfers heat from said capacitor pack to said containerend walls, and said container side walls are free to flex inwardly intosaid spaces during thermal contraction of the dielectric liquid therein.

13. Electrical capacitor comprising a rectangular container having apair of opposite side walls adapted to flex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack includinginsulating covering thereon immersed in said dielectric liquid andadapted to produce heat during operation thereof, said capacitor packbeing spaced from said opposite container side walls so as to definetherewith spaces occupied by said dielectric liquid, heat conductingmetal plate means arranged between said capacitor pack and saidcontainer substantially surrounding said capacitor pack, said metalplate means having main portions in said spaces in constant contact withsaid capacitor pack and other portions adjacent said container endwalls, and resilient means arranged between said container side wallsand said main portions of said metal plate means for urging said mainportions in constant contact with said capacitor pack, whereby duringoperation of said capacitor said metal plate means transfers heat fromsaid capacitor pack to said container end walls, and said container sidewalls are free to flex inwardly into said spaces during thermalcontraction of the dielectric liquid therein.

14. Electrical capacitor comprising a rectangular container having apair of opposite side walls adapted to fiex with variation in capacitortemperature and opposite end walls joining said side walls, a dielectricliquid in said container, a rectangular capacitor pack including aninsulating covering thereon immersed in said dielectric liquid andspaced from said opposite container side walls so as to define therewithspaces occupied by said dielectric liquid, said capacitor pack producingheat during operation thereof, and aluminum plate means arranged etweensaid capacitor pack and said container substantially surrounding saidcapacitor pack, said aluminum plate means having main portions in saidspaces in constant contact with said capacitor pack and having otherportions adjacent said container end walls, whereby during operation ofsaid capacitor said aluminum plate means transfers heat from saidcapacitor pack to said container end walls and said container side wallsare free to flex inwardly into said spaces during thermal contraction ofthe dielectric liquid therein.

15. Electrical capacitor comprising a rectangular container having apair of opposite side walls adapted to flex with variations in capacitortemperature and opposite end walls joining said side Walls, a dielectricliquid in said container, a rectangular capacitor pack including aninsulating covering thereon immersed in said dielectric liquid andspaced from said opposite container side walls so as to define therewithspaces occupied by said dielectric liquid, said capacitor pack producingheat during operation thereof, and aluminum heat conducting plates ar-'ranged between said capacitor pack and said container substantiallysurrounding said capacitor pack, said aluminum plates having mainportions in said spaces in constant contact With said capacitor pack andhaving other portions adjacent said container end walls, whereby duringoperation of said capacitor said aluminum plates transfer heat from saidcapacitor pack to said container end walls and said container side wallsare free to flex inwardly into said spaces during thermal contraction ofsaid dielectric liquid therein.

(References on following page) References Cited by the Examiner UNITEDSTATES PATENTS FOREIGN PATENTS 648,028 12/1950 Great Britain.

v 521,997 2/1956 Canada.

5 OTHER REFERENCES D y e a 31710b Marbury R. E.: Power Capacitors,McGraw-Hill, New

6mm York, 1949 QC587M3, page 9.

Lunderholm 317-243 Twaddell et a1 317243 JOHN F. BURNS, PrimaryExaminer.

Hammer 3172 10 E, JAMES SAX, Examiner.

1. ELECTRICAL CAPACITOR COMPRISING A CONTAINER HAVING A PAIR OF OPPOSITESIDE WALLS AND A PAIR OF OPPOSITE END WALLS JOINING SAID SIDE WALLS, ADIELECTIC FLUID IN SAID CONTAINER, A CAPACITOR PACK WHICH PRODUCTS HEATDURING CONATION THEREOF IN SAID DIELECTIC FLUID THEREBY CAUSING THERMALEXPANSION AND CONTRACTION OF SAID DIELECTRIC FLUID, AND CAPACITOR PACKBEING SPACED FROM SAID OPPOSITE SIDE WALLS OF SAID CONTAINER SO AS TODEFINE THEREWITH SPACES OCCUPIED BY SAID DIELECTRIC FLUID, SAIDCONTAINER SIDE WALLS BEING FREE TO FLEX INWARDLY INTO SAID SPACES DURINGTHERMAL CONSTRATION OF SAID DIELECTRIC FLUID, AND METAL HEAT CONDUCTINGMEANS ARRANGED BETWEEN SAID CAPACITOR PACK AND SAID CONTAINER HAVINGMAIN PORTIONS IN SAID SPACES IN CONSTANT CONTACT WITH SAID CAPACITORPACK AND HAVING OTHER PORTIONS IN PHYSICAL CONTACT WITH SAID CONTAINEREND WALLS, WHEREBY